The Influence of an Abrupt Convergence on Heat Transfer in Circular Ducts

The effect of an abrupt convergence on the local heat transfer coefficient at the entrance of a uniformly heated straight pipe has been investigated. Experiments were carried out with water for Reynolds numbers from 200 to 2000, and for Prandtl numbers 4 and 6. The experimental values of the local Nusselt number are considerably lower than expected and strongly Reynolds number dependent in the region near the inlet, whereas they become comparatively high further downstream. This behaviour is discussed in connection with the hypothesis of the occurrence of a separated flow at the inlet section of the pipe. These and several previous experiments, covering turbulent and transitional flows, have been considered and summarised to obtain a general view of the effect of this geometrical configuration on heat transfer